Electron discharge tube for ultra high frequencies



1947- F. D. GOODCHILD ETAL 2,426,198

ELECTRON DISCHARGE TUBE FOR ULTRA HIGH FREQUENCIES Filed Sept; 9, 1942 2Sheets-Sheet].

Arm/wa y Aug. 26, 1947. F. D. GOODCHILD ErAL 2,426,198

ELECTRON DISCHARGE TUBE FOR ULTRA HIGH FREQUENCIES v Filed Sept. 9} 19422 Sheets-Sheet 2 m Eurons 8) M1,) 4 Mina Array/w y Patented Aug. 26,1947 ELECTRON DISCHARGE TUBE FOB ULTEA HIGH FREQUENCIES Frank DouglasGoodchild and Willem Harry Wolsey, London W. C. 2, England, assignors toStandard Telephones and Cables Limited, London, England, a Britishcompany Application September 9, 1942, Serial No. 457,791 In GreatBritain October 24, 1941 6 Claims.

This invention relates to improvements in electron discharge tubes forultra high frequencies of the type disclosed in United Statesapplication Serial No. 445,509.

The tube disclosed in the above application consists of a bulb having acopper disc sealed in the middle, a stem carrying the grid and cathodesealed at one end and another stem carrying the anode sealed at theopposite end. When working in the 10 cm. range there are certainlimitations of the tube, and the present invention has for its mainobject to provide an improved construction in which these limitationsare avoided by ensuring that the current path from the centre of thegrid wires to the screening disc is as short and direct as possible, andthus the contact springs providing contact between the grid and thescreening disc, which have been found to be a source of loss whenworking in this range, are dispensed with. Furthermore, the connectionto the anode must be a continuous surface of metal, and thus the thimbletype of anode which was sealed into the stem by the Housekeeper typeseal has been replaced by a tubular anode as will be hereinafterdescribed.

Accordingly the present invention provides a tube of the above type inwhich the grid is mechanically connected to the screening disc toprovide intimate electrical contact therewith, whereby the current pathfrom the centre of the grid wires to the screening disc is as short anddirect as possible.

The invention also provides a tube of the above type in which the anodecomprises a metal tube sealed into the stem and projecting outside theenvelope to provide a direct electrical connection to the anode, whichmay be formed as a speciallyshaped block which is secured in the end ofthe tube in a vacuum-tight manner.

The invention will be better understood by reference to the accompanyingdrawings, in which:

Fig. 1 is a sectional view of the improved tube;

Fig. 2 is an exploded view thereof;

Fig. 3 shOWs a preferred construction of the anode;

Fig. 4 shows a detail ofFig. 3;

Figs. 5 and 6 show respectively a plan view of the stem which supportsthe cathode and grid structure, having a coaxial pair of conductors.

In these drawings, l and 2 represent the cylindrical glass envelopeportions, and 3 the copper screening disc which is sealed between themand which extends well beyond the glass envelope portions to form aneffective screen between the two halves of the tube, and also to providea mounting device for connecting the tube directtly in the grid circuit.The center of the disc is provided with an aperture i to accommodate thegrid 5 which is constructed as follows. A grid unit is formed by takinga normally-wound grid made, for example, by the notch and swage methodof 250 turns per inch of 0.001 inch tungsten wire wound on two nickelsupport rods 6. The grid wires on one side are cut away and the halfgrid so formed is then brazed on to a square of thick nickel ormolybdenum sheet I, which is apertured at 8 to provide the grid opening,and which is provided with four locking and fixing holes 9 by which itis supported at four points on the pillars It provided on the specialfour-pillar stem H. The cathode I2 is also supported on this stem and asshown consists of a tubular member supported at its middle by a singlewire support is.

In assembling the valve a bulb having the screening disc 3 sealed at thecentre is taken and the stem H is pushed in through one end. The fourpillars l0 protruding through the holes 9 in the grid plate 1 then passthrough corresponding holes I in the screening disc 3 and are secured bycollars IE on the opposite side, the welding electrodes for securing thecollars being passed into the open end of the envelope portion 2. Thisarrangement ensures good electrical contact between the grid unit andthe copper screening disc. Two of the pillars 10 also carry a micabridge piece Hi which is apertured at I1 and forms an anode guide aswill be hereinafter described. This bridge piece is secured to thepillars after the connection between the grid unit and the screeningdisc previously described has been completed.

For the anode, a new type of stem has been developed which consists ofglass moulded to the outside of a thin-wa1l copper tube IS. The anodeproper consists of a block l9 secured by hard soldering into the innerend of the tube l8 and forming a vacuum-tight joint therewith. As shown,the anode is rectangular in shape and is provided with shoulder pieces20 which co-operate with the mica bridge piece l6 previously described,and which ensures accurate spacing between the anode and grid, when theanode stem is sealed into the envelope portion 2. It will be seen thatwith this construction a direct electrical connection is made with theanode through the anode stem it which projects beyond the envelope ofthe tube.

In the improved construction of anode shown in Fig. 3, a rod 2| ofcopper or other metal shown also in Fig. 4, is inserted into the tube 18and is secured rigidly to the block 19 in any suitable way, butpreferably by means of a screw 22, as shown. The rod 21 is preferablymade a snug fit in the tube 18, but its diameter should preferably beslightly reduced at 23, in the neighbourhood of the seal, in order toprevent the seal from being cracked by the expansion of the rod when theanode become heated. The rod 2| may be provided with a screwdriver slotas shown at 24.

It will be seen that with this arrangement, very good thermal contact ismade with the block 19, which is the anode proper of the discharge tube,so that the heat is much more quickly conducted away than by the ratherthin copper tube alone. When working in the cm. range for example it isoften necessary or desirable to bring the wave energy to and from thetube by means of coaxial conductors. In order that this may beefiiciently done, a coaxial conductor should be brought inside the tubeand as close as possible to the cathode. The construction shown. inFigures 5 and 6 cmbodies this feature.

Referring to Figures 5 and 6, through the centre of the stem H is sealeda tube 25, preferably of copper, and inside the tube is sealed a rod orwire conductor 26 by means of a glass bead 21, which may be at the upperend, as shown, or elsewhere. The tube 25 and the conductor 26 constitutea coaxial conductor system which extends inside the discharge tube whenthe stem ii is sealed into the bulb, all the joints being vacuum-tightWhat is claimed is:

1. An electron discharge tube comprising an envelope, an apertured metalscreening plate extending transversely across said envelope and sealedthrough the walls thereof to divide said envelope into two portions, ananode in one portion and a cathode in the other portion, the saidcathode being mounted on a stem. carrying a plurality of pillars, a gridelement comprising grid wires secured to an apertured metal plate, saidplate being mounted on said pillars, and means on said pillars securingsaid metal plate to said metal screening plate.

2. An electron discharge tube according to claim 1 wherein the leads forthe cathode comprise a coaxial pair of conductors, said coaxial pair ofconductors comprising a metal tube sealed through the stem on which saidpillars are mounted and a conductor coaxial with the tube insulatedtherefrom and sealed therein by means of a glass bead seal.

3. An electron discharge tube in accordance with claim 1 including aguide member supported by at least some of said pillars and engagingsaid anode to locate the latter with respect to said grid element.

4. An electron discharge tube in accordance with claim 1 wherein thegrid element comprises a pair of support rods attached to the aperturedmetal plate and grid wires extending between said support rods.

5. An electron discharge tube comprising an envelope, a grid supportsealed into the envelope transversely thereof, a grid carried by saidsupport, an anode on one side of said grid, a cathode on the other sidethereof, a stem carrying a plurality of pillars, means attaching saidgrid support to said pillars, and an anode guide mounted on said pillarsand engaging said anode to locate the latter with respect to said grid.

6. A lead-in conductor assembly for electron discharge devices,comprising a thin-walled metal tube with an external glass sealing areaintermediate the ends of said tube, an electrode, adapted to be heated,attached to one end of said tube, said one end of the tube beinghermetically closed, a solid rod of good heat conducting metal extendingthrough said tube and in good heat transfer contact with said electrodeand with the inside surface of said tube substantially throughout thelength of said tube, said rod being out of contact with said tubeopposite said glass sealing area.

FRANK DOUGLAS GOODCHILD. WILLEM HARRY WOLSEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,034,433 Heinz Mar. 17, 19362,136,448 Lindenblad Nov. 1 5, 1938 2,280,980 Samuel Apr. 28, 19422,303,166 Laico -1 Nov. 24, 1942 2,167,201 Dallenbach July 25, 19391,717,309 Bouwers June 11, 1929 1,190,104 Campbell July 4, 19161,564,690 Kruh et a1 Dec. 8, 1925

